JP 2008-170455 A discloses a displacement amount monitoring electrode arrangement for an angular velocity sensor, etc., which is configured to monitor a displacement amount of a detection mass so as to drive the detection mass with constant target amplitude. The displacement amount monitoring electrode includes a fixed electrode with a comb shape and a movable electrode with a comb shape. The fixed electrode is formed by a base portion and plural electrode fingers extending from the base portion in a predetermined axis direction, and is fixed with respect to a substrate. The movable electrode is formed by a base portion and plural electrode fingers extending from the base portion in the predetermined axis direction parallel to the substrate, and is movable in the predetermined axis direction with respect to the substrate. In such a displacement amount monitoring electrode, when the movable electrode is displaced in the predetermined axis direction with respect to the substrate, a capacitance between the fixed electrode and the movable electrode changes. At that time, a change amount of the capacitance depends on the displacement amount of the movable electrode. Then, the displacement amount (amplitude) of the detection mass is monitored based on the change amount of the capacitance, and the detection mass is controlled such that it is driven to have target amplitude.
In general, the change amount of the capacitance between the fixed electrode and the movable electrode changes linearly with the amplitude of the detection mass; however, it changes because of not only the amplitude of the detection mass but also a gap and an opposed area between the fixed electrode and the movable electrode. Specifically, if the gap and the opposed area change due to variations in stress or dimensions, etc., sensitivity (i.e., a gradient) of the change amount of the capacitance with respect to the displacement amount of the movable electrode changes accordingly. According to a configuration in which a target capacitance change amount of the capacitance when the detection mass is driven with the target amplitude (i.e., when the displacement of the movable electrode in the predetermined axis direction reaches a target displacement amount corresponding to the target amplitude) is set in the linear change region in which the change amount of the capacitance changes linearly with the displacement of the movable electrode, if the gap and the opposed area don't match with desired values due to the stress applied at the time of assembling the monitoring electrode, temperature change, variation in the dimensions, etc., there may be a case where the displacement amount of the movable electrode does not match the target displacement amount when the change amount of the capacitance reaches the target capacitance change amount, which makes it difficult to keep the amplitude of the detection mass at a constant target amplitude.